In general, a vehicle generates noise due to engine explosion, intake operation, exhaust operation, friction with air while driving, road, etc.
The exhaust noise includes pulsation noise, flow noise, etc. which are generated mainly due to pressure differences. An exhaust system is in general provided with a muffler to reduce such exhaust noise. However, it is more effective to damp the flow noise of the exhaust system near an engine side, e.g., an exhaust manifold, than in the muffler.
FIGS. 1(A) and 1(B) show exhaust system structures according to a prior art and an exemplary embodiment of the present inventive concept, respectively.
FIG. 1(A) shows an exhaust manifold 10 of an exhaust system according to the prior art.
Exhaust noise, which is caused due to explosion strokes while driving, is collected to a collector 30 through runners 15 of the exhaust manifold 10 and passes through a front pipe 20 to be transferred towards a muffler (not shown).
In this case, a shrink-type collector 30, which has radii decreasing in a direction towards noise transfer, is used in order to naturally connect the runners 15 and the front pipe 20.
Each runner 15 is provided to improve performance of an engine. However, considerably large noise is caused in the collector 30, into which the noises are collected by high-speed exhaust gas, by an increase of jet velocity and generation of vortex. Here, a noise level inside the front pipe 20 as in volume acoustic power (VAP), which is turbulent noise energy per unit volume, reaches 143 dB which is considerably high.
The noise is recognized as rough noise in a gradual acceleration condition of 1500-3000 rpm, thereby causing drivers' dissatisfaction.
Therefore, modification of an exhaust system structure to overcome this kind of problem is necessary. Turbulent flow noise is inevitably generated in the exhaust system according to the prior art, thereby deteriorating marketability of a vehicle.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.